1. Field of the Invention
The invention relates to a data driver and related method for driving data, and more particularly, to a digital data driver and related method for driving at least a data line of a display device to save space and to pre-charge the data line.
2. Description of the Prior Art
Liquid display devices (LCD), which are thin, flat panel display devices, can be found in a plethora of electronic goods, ranging from notebook computers and digital cameras to flight avionics and medical diagnostic tools. LCDs offer crisp, high-resolution images, and have the primary advantage of offering relatively low power-consumption rates while still maintaining good color contrast and screen refresh rates. In recent years, the newly developed low-temperature Poly Silicon LCD (LTPS LCD) can directly attach the driving circuit on the glass substrate so that the quantity of the driving circuits can be reduced, the package/material cost can be downsized, and the reliability and compactness of the commercialized products can be significantly increased.
The LCD system can be separated into “digital type” and “analog type” according to different types of input data. For achieving advantages of power saving, integrity, and cost effectiveness, more LCD systems adopt the digital type of input data so that the digital-to-analog converter should be involved in the data driver. For matching the digital-to-analog transformation, some latch circuits or sample/hold circuits should be integrated into the data driver and installed before the corresponding digital-to-analog converter. Please refer to FIG. 1, which is a functional block diagram of a prior-art data driver 10. The data driver 10 corresponds to the three ingredient colors R, G, B of a pixel 11 of a display device. The data driver 10 includes an input module 12, two grades of latches 14, 16 (first-grade latches 14 and second-grade latches 16), a shift register 11, and three digital-to-analog converters 20r, 20b, 20g. The input module 12 includes three N-bit circuit lines 12r, 12b, 12g, and each N-bit circuit line can be used to receive an N-bit digital data set. Each N-bit digital data set corresponds to one of the three ingredient colors R, G, B of the pixel 11 of the display device (the N-bit digital data set DR0–DR5 corresponds to the ingredient color R of the pixel 11; the N-bit digital data set DB0–D5B corresponds to the ingredient color B of the pixel 11; the N-bit digital data set DG0–DG5 corresponds to the ingredient color G of the pixel 11). N is an integer whose value is greater than or equal to 2. As shown in FIG. 1, N is defined as 6, that is, each digital data set is the 6-bit digital data set. Two grades of latches 14, 16 are electrically connected to the input module 12 for level shifting and buffering. Each grade of latches includes three latches that respectively correspond to the three ingredient colors R, G, B of the pixel 11 (the first-grade latches 14 include three latches 14r, 14b, 14g, and the second-grade latches 16 include three latches 16r, 16b, 16g). Each latch can be used to temporarily store the N-bit digital data set so that each latch is designed as an N-bit latch. The shift register 18 can output a switch signals SR to transmit the N-bit digital data set, which corresponds to the three ingredient colors R, G, B of the pixel 11, at one time to the first-grade latches. The first-grade latches 14 will execute the level-shifting and buffering functions. Afterwards, the N-bit digital data set will be transmitted to the second-grade latches 16 that still execute level-shifting and buffering functions. The digital-to-analog converters 20r, 20b, 20g are electrically connected to the second-grade latches 16 for receiving the N-bit digital data set outputted from the second-grade latches 16 and for transforming the N-bit digital data set into an analog voltage signal. The analog voltage signal the will be applied to the data lines 22r, 22b, 22g. The color displaying performance of the display device depends on the amplitude of the analog voltage signal. Usually, a switch LP is installed between the first-grade latches 14 and the second-grade latches 16 of the data driver 10 to control the time by which the N-bit digital data set temporarily stored in the first-grade latches 14 can be one-time transmitted to the second-grade latches 16 so that the charging time in the digital-to-analog converters 20r, 20b, 20g can be well controlled and sufficient. The above-mentioned prior art related to the digital data driver has been disclosed in some prior patents and documents. Yojiro Matsueda et al. presented that the data driver can be fabricated on the glass substrate by LTPS technique and a novel digital 6-bit data driver is achieved in 96 Digest, “Low Temperature poly-Si TFT-LCD with integrated 6-bit Digital data driver”. In addition, for improving the data transformation process, they integrated the related latch circuits into the data driver and installed the latch circuits in front of the digital-to-analog converters.
From the above-mentioned prior art, for temporarily storing the N-bit digital data set in the digital data driver, each latch should be designed as an N-bit latch. Nowadays, because the users require finer display quality, the display device should be designed with more delicacy. For instance, if a display panel is equipped with a 4096-color performance, the digital data set should be the 4-bit digital data set. Then the data driver should comprise 4 bit digital-to-analog converters and 4-bit latch circuits. Similarly, if a display panel is equipped with a 262144-color performance, the digital data set should be the 6-bit digital data set. In the meanwhile, the data driver should comprise 6-bit digital-to-analog converters and 6-bit latch circuits. However, with better dpi-performance (dots per inch) of the display panel, the space for each pixel should be reduced so that the space for accommodating the data driver is constrained. Therefore, two different solutions are raised in order to solve the problem. Instead of fabricating the data driver on the glass substrate by LTPS technique, the first solution adopts adhering the data driver on the glass substrate as a typical a-Si LCD process. The first solution still leaves lots of doubts in tolerating temperature fluctuations and lacks many advantages of LTPS technique in small/middle-size-panel applications. Morita et al. in Toshiba Corp. suggested a selecting circuit so that the circuit designer can share the functions of the digital-to-analog converters and latch circuits so as to reduce the space occupation of the data driver in an academic document, “A 2.15 inch QCIF reflective color TFT-LCD with integrated 4-bit DAC driver”, IDW '00, pp. 1149–1150. Therefore, the quantity of the digital-to-analog converters and latch circuits can be greatly reduced. However, each latch circuit still has to process the same bit number as that of each digital data set. That is, if the digital data set is a 4-bit digital data set, the corresponding latch circuit should be a 4-bit latch circuit. Similarly, if the digital data set is a 6-bit digital data set, the corresponding latch circuit should be a 6-bit latch circuit. Therefore, the design of the prior art still leaves a lot of room for improvement in saving circuit space.